Beijing Key Laboratory for Source Control Technology of Water Pollution, Engineering Research Center for Water Pollution Source Control and Eco-remediation, Beijing Forestry University, Beijing 100083, China; College of Environment, Zhejiang University of Technology, Chaowang Road 18, Hangzhou 310014, China.
Beijing Key Laboratory for Source Control Technology of Water Pollution, Engineering Research Center for Water Pollution Source Control and Eco-remediation, Beijing Forestry University, Beijing 100083, China.
Sci Total Environ. 2021 Dec 1;798:149001. doi: 10.1016/j.scitotenv.2021.149001. Epub 2021 Jul 13.
In algae rich waters, sunlight-driven transformation of antibiotics could be accelerated via sensitization by algae extracellular organic matter (EOM), and this photosensitization process will be affected by coexisting humic substances. In this study, we explored the effect and mechanism of humic substances on photodegradation of chlortetracycline (CTC) mediated by EOM. We found that humic substances exhibited a marked inhibitory effect on the EOM-mediated photodegradation of CTC. Given that humic substances exhibited little effects on the EOM-mediated formation of triplet state species, the quenching effect of humic substances on reactive species was excluded. The inhibitory effect of humic substances was mainly attributed to the back reduction of CTC oxidation intermediates by the antioxidant moieties in humic substances. The ozone oxidation treatment for humic substances was applied to destroy antioxidant moieties. After ozonation, the inhibitory effects of humic substances were greatly decreased, confirming the dominant role of antioxidant moieties in humic substances, which inhibited CTC photodegradation mediated by EOM via reducing oxidation intermediates of CTC. This back reduction was further verified to be exergonic via reactive Gibbs free energy, indicating the back reduction by humic substances of CTC oxidation intermediates could occur spontaneously. The present study will be helpful for predicting the fate and risk of CTC in algae rich water environments, and is of great significance for the study of phototransformation of other antibiotics.
在富藻水中，抗生素的阳光驱动转化可以通过藻类细胞外有机物 (EOM) 的敏化作用加速，并且这个光敏化过程将受到共存的腐殖质的影响。在这项研究中，我们探讨了腐殖质对 EOM 介导的土霉素 (CTC) 光降解的影响和机制。我们发现腐殖质对 EOM 介导的 CTC 光降解表现出明显的抑制作用。鉴于腐殖质对 EOM 介导的三重态物种形成几乎没有影响，排除了腐殖质对活性物质的猝灭作用。腐殖质的抑制作用主要归因于腐殖质中的抗氧化部分对 CTC 氧化中间产物的反向还原。应用臭氧氧化处理腐殖质以破坏抗氧化部分。臭氧化后，腐殖质的抑制作用大大降低，这证实了腐殖质中抗氧化部分的主要作用，它通过还原 CTC 的氧化中间产物来抑制 EOM 介导的 CTC 光降解。通过反应吉布斯自由能进一步证实了这种反向还原是放能的，表明腐殖质对 CTC 氧化中间产物的反向还原可以自发发生。本研究将有助于预测富藻水中 CTC 的命运和风险，对于研究其他抗生素的光转化具有重要意义。
